Chair frame construction



Sept. 22, 1959 E. F. UMPHRED, JR., T L ,905, CHAIR FRAME CONSTRUCTION Filed April 22, 1955 IN VEN TORS ED W/N f-T UMPHRED JR.

EVER/VEST L. PACE .4 TTO/PNE Y5 United Stat CHAIR FRAME CONSTRUCTION Application April 22, 1955, Serial No. 503,202 4 Claims. (Cl. 155-196) This invention relates to a new and useful chair frame construction and in particular to a novel means for giving increased strength and rigidity to the chair where the seat frame portion is joined to the rear legs.

Most chairs are weak at the point of juncture of the seat frame with the back legs and rail. In orthodox construction the side rails or supports for the seat are secured to the rear or back legs, the former abutting the front face of the latter. Excluding the nominal rigidity resulting from the junction of the seat with the back rail or support, in conventional chair structure the rigidity of the seat and front legs relative to the back legs is solely dependent on the strength of joinder of the side rails with the back legs. As is generally known, weight shifts by the seated person and particularly tilting back of the chair with accompanying leverage at the point of juncture of side rail and leg may rapidly loosen the side rails from the back legs and result in shearin the members apart.

A number of devices and designs have been used in an effort to remedy this problem, including various nut and bolt arrangements at the said points of side rail and back leg juncture, shortening the seat to decrease leverage, and also horizontal braces or stretchers between the front and rear legs at spaced distances below the seat. The stretchers in conjunction with the legs and the side rails of the 'seat resist distortion and hence resist downward movement of the front of the seat relative to the said juncture points.

The foregoing efforts have generally proven inadequate. The stretchers', which best render the chair substantial, are objectionable in that they are expensive in labor and material, interfere with cleaning under the chairs, increase storage and shipping problems and are not desirable from the standpoint of good design.

. It isthe object of this invention to provide a substantial chair capable of standing up under home and commercial use and of sufiicient strength and rigidity so that stretchers and like known devices are rendered unnecessary.

Other more specific objects will become apparent upon reference to the specification and accompanying drawings in which similar characters of reference represent corresponding parts in the several views.

In the drawings:

Fig. 1 is a fragmentary, exploded perspective view of a detail showing a preferred embodiment of the invention;

Fig. 2 is a fragmentary side elevation, partly in section, of the same;

Fig. 3 is a top plan view, partly in section, of a chair frame employing the novel construction; and

Fig. 4 is a fragmentary perspective of a chair.

The drawings illustrate a chair frame comprising two front legs 2 and 3, two back legs 4 and 6, a front rail 7, a back rail 8, a top back rail 9, and two side rails 11 and 12.

The front rail 7 is secured at either end to a front leg adjacent the top of the latter, as by a suitable glue 2,9@5,232 Patented Sept. 22, 1959 or cement applied to obverse areas of contact. Dowel pins or other connecting means of joinder may be used, as for example, wood screws. The side rails 11 and 12 are similarly secured at one end respectively to the front legs 2 and 3 extending rearwardly therefrom, and corner blocks 13 are secured as by screws 14 at the formed interior corners for additional strength. The construction thus far described is conventional.

The illustrated embodiment discloses a chair frame wherein the back legs 4 and 6 are displaced angularly relative to the side rails 11 and 12 such that the projected longitudinal axis of each side rail is disposed at an acute angle to the inner side faces 4a and 6a of the adjacent back legs 4 and 6. The acute angle is indicated at X in Fig. 3. Such displacement increases the aesthetic appearance of the chair design but tends to weaken the connection of back leg and side rail. The present inven tion provides an improved chair construction wherein the point of juncture of back leg and side rail is materially strengthened over conventional chair construction, particularly where the back legs are displaced angularly relative to the side rails as above noted.

The drawings and description herein presume a wood construction.

The invention resides in the construction at the juncture of the back rail 8 and back legs 4 and 6 with the side rails 11 and 12. The side rails are preferably about twice as thick as the back legs to which they are attached, and the back rail, as illustrated, has a thickness substantially one-half the width of the back legs. The back rail 8 is secured as by dowel pins 16 and a suitable glue or cement to the back legs 4 and 6 abutting the latter at points rearward of the front face 17 of the back legs. The longitudinal axes of the back and front rails are substantially parallel. The rearward bow of the back rail is entirely a matter of taste and is in no way critical to the invention.

Each side rail 11 and 12 is angularly notched or recessed substantially one-half its thickness adjacent its rear end to provide a lap butt 18 against the rear legs 4 and 6, the end 19 of the lap 18 being beveled to accommodate the bowed back rail 8 and provide a flush abutment thereagainst. The butt 19 is secured by suitable means as by glue and dowel pins to the front face 17 of the back leg 4. Obverse surfaces of contact, viz., the face 18b of the lap 18 contacting the adjacent inner side face 4a and 6a of each back leg 4 and 6 and the end 18b of the lap 18 and the abutted area of the back rail 8, are similarly rigidly secured as by glue and dowel pins or wood screws. Conventional corner blocks 23 may be secured to the formed interior corners.

As previously noted, in conventional construction the only resistance to the downward force on the seat caused by the seated person is at the point of juncture or joinder of the side rails with the back legs. In the construction of the present invention, the downward force is substantially equally resisted at the following three points: at the joinder of the butt 19 with the front face 17 of each back leg 4 and 6; at the joinder of the back rail 8 with the ends 18a of side rails 11 and 12; and at the joinder of the face 18b of the lap 18 with the inner side or face 4a and 6a of each back leg 4 and 6. The division of work between the said three points is approximately equal. Thus the strength of the chair is substantially tripled over the orthodox or conventional construction.

In the event the chair is subjected to sulficiently eX- treme leverage to loosen or shear the butt 1% from the front 17 face of the back legs 4 and 6, an interesting and novel transmission of forces takes place. This is illustrated schematically in Fig. 2 wherein arrow A represents the downward force of the seated person, arrow B indicates the initial point at which shear will occur, arrow C indicates the fulcrum about which the loosened side rail 11 will pivot, and arrow D represents the transmitted upward force focusing at the joinder of the back rail 8 with the back leg 4. As force A is exerted on side rail 11 the resultant leverage focuses at the juncture of the butt 19 with the front 17 of the back leg 4; the side rail 11 pivots around fulcrum C causing shear commencing at B. The end 18a of the lap 18, however, is secured to the abutted back rail 8. Hence the downward force A which has tended to weaken the chair at B is transmitted into a substantially equal upward force D focusing at the firm joinder of the back rail 8 with the back leg 4. Other features of the invention lend additional resistance to the forces and consequent tendency for pivotal movement of the side rails relative to the back legs. One such feature is the joinder of the face 18b of the lap 18 with inner side face 42 of back leg 4.

In the form of chair construction as shown in the drawing, the longitudinal axes of side rails 11 and 12 converge backwardly toward one another. The back legs 4 and 6 are disposed relative to the said rails in such a way that the longitudinal axes of side rails form an angle acute to the inner faces 4a and 6a of said legs. It is an extremely important aspect of the invention that the face 18b of the lap joint forms a wedge joint defined by the back rail and adjourning back leg. As particularly illustrated in Figs. 1, 3 and 4, the lap is angularly disposed to be thicker at its end 18a than at the butt 19. The assembled chair frame, illustrated in Figs. 3 and 4, show the lap 18 wedged or locked between the side rail 11 and a corner block 23. The wedge joint thus formed accomplishes a wedge action between the lap and associated legs and back rail and prevents pivotal relative displacement or pivotal movement of the rail in respect to its associated leg.

As a consequence of the rigidity and strength of this construction, the chair will stand up under considerable abuse. The objectionable and expensive stretchers are rendered unnecessary and the appearance of the chair is greatly increased.

The foregoing description has been in some detail by way of illustration and example to augment clarity. It will be understood that certain changes and modifications may be made without departing from the spirit of the invention or scope of the appended claims.

What is claimed is:

1. In a chair frame construction of the type including front and back legs, a back rail and side rails, means to join the front legs together and to the side rails the improvement comprising: the back rail secured to the back legs inwardly of the front face thereof; the inner faces of each of the back legs disposed at an angle whereat the front portion of the inner side face of the leg is substantially further inward than the rear portion; each said side rail formed adjacent its rear end to define a lap butt to provide a snug fit against the front and inner side face of a back leg and adjacent inner face of the 4 back rail; and means to prevent relative transverse movement of said side rails with respect to said legs whereby the said lap butt forms a wedge lock to prevent relative longitudinal movement of said side rail with respect to said leg.

2. In a chair frame construction of the type including front and back legs, a back rail and side rails, means to join the front legs together and to the side rails the improvement comprising: said back rail secured to said back legs rearwardly of the front face thereof; the ends of said back rail being provided with a pair of inwardly projecting protuberances; each protuberance disposed in spaced relation with a said rear leg to define a recess between the inner side face of said leg and a first side face of said protuberance which faces the inner side face of said leg; the first side face of said protuberance and the inner side face of said leg relatively angled wherein the throat of the recess is substantially smaller than the portion of the'recess adjacent the back rail; each said side rail formed adjacent its rear end to define a lap butt shaped to snugly fit within the recess wherein the side walls of the butt lie adjacent the first face of the protuberance, the inner face of the back rail, and the inner side face of the back leg; and wherein said butt has a surface portion formed exteriorly of the recess to snugly fit against the front side face of said back leg.

3. A chair frame according to claim 2 and wherein the first faces of said protuberances are axially aligned with the inner side faces of said side rails and the inner side faces of said rear leg are acutely angled relative to the longitudinal axis of said rail.

4. In a chair frame construction of the type including front and back legs; a back rail and side rails, the improvement comprising: the inner face of each of the back legs disposed at an angle whereat the front portion of the inner face of each said leg in disposed substantially further inward than the rear portion thereof, each said side rail formed adjacent its back end to define a lap butt to provide a snug fit against the front face and the inner face of a back leg; each end of said back rail snugly abutting the inner face of a back leg; .the back end of each said side rails snugly abutting the inner side of the back rail; and means comprising said lap butt to join said side rails, back rail and back legs in relatively fixed position with respect to one another.

References Cited in the file of this patent UNITED STATES PATENTS 172,724 Eno Jan. 25, 1876 220,245 Lee Oct. 7, 1879 1,292,090 Schimmel Jan. 21, 1919 1,480,905 Hebert Jan. 15, 1924 2,552,286 -Kompass May 8, 1951 FOREIGN PATENTS 3,872 Great Britain 1907 

